The Milwaukee Road's Chicago-Twin Cities Hiawatha proved so popular that longer trains were needed, beyond the ability of the class A 4-4-2s to handle. In 1938 Alco erected six class F-7 4-6-4s to take over the service. With smaller-diameter 23½x30 cylinders and higher 84-inch drivers than the Milwaukee's earlier so-called "Baltics," the F-7s compensated with a high 300-pound boiler pressure. They produced 50,300 pounds of tractive force, and weighed 415,000 pounds without tender. Their large 96½-square-foot grate area combined with
an evaporative heating surface of 4166 square feet and 1695 square feet of superheating surface to create the steam capacity for their premier high-speed service. However, once diesel power took over the Hiawathas these shrouded Hudsons were found not as well suited to other duties as the earlier 4-6-4s. As a result they met an early demise, all being consigned to the scrapyard by the end of 1951. Carl Weber contributed this photo of F-7 No. 104 in Chicago on November 24, 1938, not long after delivery from the builder.